On the horizon

Cleaning a lake with carp

For years men and machines have toiled to clean up Kashmir's mirror-calm Dal Lake to remove choking weeds, lily pads, and other water plants that have tarnished the image of the famed tourist attraction.

But scientists in the Indian Himalayan region have hit upon a new low-cost idea: flood the dying lake with thousands of weed-eating Chinese grass carp. A small number of the Chinese fish, which only eat water plants, had been released in pens at a few places in the lake in tests.

"It will be able to control the growth of weeds, but the plants won't completely vanish from the whole lake," said Moulvi Manzoor, deputy director of Jammu and Kashmir state's fisheries department.

The lake, which once covered 12 square miles, has shrunk to half that size over the past four decades because of silt, weeds, and development.

Weeds have flourished in the lake because of the large amounts of waste flowing into it. Civic authorities say they will build six sewage-treatment plants around the lake to stop the waste being discharged from the houseboats, hotels, and houses on its banks.

Each year, authorities remove more than 6,500 metric tons of weeds using floating de-weeding machines. Laborers also manually remove the plant menace from the lake.

Mr. Manzoor said the grass carp has been successfully used for biological weed control in the United States and Europe. The fisheries department has imported more than 10,000 fish from China and also set up a breeding center in Kashmir.

But one expert said the fish would affect the lake's ecosystem and might not be able to attack all 25 types of weeds that thrive in the lake. "Grass carp is selective in eating. It prefers softer weeds," said Nissar Jan, former chief of the state's fisheries department. "The fish can change the nutrient balance of lake. Grass carp also leave huge excreta which would pollute it more."

Harmful ozone from a brown, smoggy cloud of pollution that hovers over South Asia and the Indian Ocean has spread thousands of miles to Africa and Brazil, according to NASA scientists who tracked the pollution with satellites and special weather balloons.

The scientists, who released their findings last week at an American Geophysical Union meeting in San Francisco, said the smog's dispersal was significant because the ozone can burn people's lungs and damage crops.

Robert Chatfield, a scientist at NASA's Ames Research Center in Moffett Field, Calif., said he had spent five years examining how clouds suck in ozone and small particles and then transport them at the same altitude where jets fly over long distances. "Our regional smog effects have global consequences," Mr. Chatfield said. "I was surprised to find out how far the pollution could go."

The ozone-monitoring equipment on NASA's Aura satellite is key to providing the data, Chatfield said.